Electronic Devices - Online Test
Q1. In the circuit below, the diode is ideal. The voltage V is given by
Answer : Option A
Explaination / Solution:
Let diode be OFF. In this case 1 A current will flow in resistor and voltage across resistor will be V = 1.V
Diode is off, it must be in reverse biased, therefore
Vi- 1 > 0 " Vi > 1
Thus for Vi > 1 diode is off and V = 1V
Option (B) and (C) doesn’t satisfy this condition.
Let Vi < 1. In this case diode will be on and voltage across diode will be zero and
V = Vi
Thus V = min(Vi,1)
Q2.
Consider the following two statements about the internal conditions in a n - channel MOSFET operating in the active region.
S1 : The inversion charge decreases from source to drain
S2 : The channel potential increases from source to drain.
Which of the following is correct?
Answer : Option D
Explaination / Solution:
Both S1 and S2 are true and S2 is a reason for S1.
Q3. 
For the NMOSFET in the circuit shown, the threshold voltage is Vth, where Vth > 0. The source voltage VSS is varied from 0 to VDD. Neglecting the channel length modulation, the drain current ID as a function VSS is represented by
Answer : Option A
Explaination / Solution:
We have the following conditions
Since it is in saturation, current ID is given by
Thus, ID - VSS graph shows Parabolic relation for Vss < VDD
- Vth and zero for Vss > VDD
- Vth. Only graph shown in option (A) satisfies this result.
Q4. In the figure, assume that the forward voltage drops of the PN diode D1 and
Schottky diode D2 are 0 7. V and 0 3. V, respectively. If ON denotes conducting
state of the diode and OFF denotes non-conducting state of the diode, then in
the circuit,
Answer : Option D
Explaination / Solution:
Alternatively, we can solve the problem by considering the current through two
diodes. Here, the correct case is only considered. 
Case : Diode D1 is OFF, D2 is ON. For this case. The equivalent circuit is
From the circuit, we have
I1 = 0
I2 = 10 - 2.3/1.02
= 9.7/1.02
= 9.5 mA
Since, the current I2 is positive, So our assumption is correct.
Q5. If fixed positive charges are present in the gate oxide of an n-channel enhancement type MOSFET, it will lead to
Answer : Option A
Explaination / Solution:
If fixed positive charges are present is the gate oxide of an n-channel enhancement type MOSFET, it will lead to a decrease in the threshold voltage.
Q6. In the following circuit employing pass transistor logic, all NMOS transistors
are identical with a threshold voltage of 1 V . Ignoring the body-effect, the
output voltages at P, Q and R are,
Answer : Option C
Explaination / Solution:
No Explaination.
Q7. The doping concentrations on the p-side and n-side of a silicon diode are 1 × 1016 cm-3 and 1 × 1017 cm-3, respectively. A forward bias of 0 3. V is
applied to the diode. At T = 300 K, the intrinsic carrier concentration of silicon ni = 1.5 × 1010 cm-3 and (kT/q) = 26 mV. The electron concentration at the edge of
the depletion region on the p-side is
Answer : Option A
Explaination / Solution:
Given the doping concentration on p-side
NA = 1 × 1016 cm-3
V = 0.3 V
Intrinsic carrier concentration,
So, the equilibrium electron concentration on the p-side is
Therefore, the electron at the edge of the depletion region on the p-side is obtained
as
Q8. The peak electric field in the device is
Answer : Option B
Explaination / Solution:
The peak electric field in device is directed from p to n and is 
Q9.
For small increase in VG beyond 1V, which of the following gives the correct description of the region of operation of each MOSFET
Answer : Option D
Explaination / Solution:
For small increase in VG beyond 1 V the n - channel MOSFET goes into saturation as VGS + ive and p - MOSFET is always in active region or triode region.
Q10.
Estimate the output voltage V0 for VG = 1.5 V. [Hints : Use the appropriate current-voltage equation for each MOSFET, based on the answer to Q.57]
Answer : Option C
Explaination / Solution:
Consider for CMOS circuit shown, where the gate voltage v0 of the n-MOSFET is increased from zero, while the gate voltage of the p -MOSFET is kept constant at 3 V. Assume, that, for both transistors, the magnitude of the threshold voltage is 1 V and the product of the trans-conductance parameter is 1mA. V-2
